1. Field of the Invention
The present invention relates to a supercharger for vehicle engines.
2. Description of the Related Art
Conventionally, there is a supercharger in which a rotation speed of an input shaft is increased by a speed increasing gear so as to be transmitted to an output shaft, and an impeller is provided in the output shaft.
In order to obtain a high speed increasing ratio, Japanese Patent Application Laid-Open No. 4-203421 proposes a structure using a planetary gear mechanism and Japanese Patent Publication No. 11-502596 proposes a structure using a planetary friction roller mechanism, as the speed increasing gear.
In the structure using the planetary gear mechanism described in Japanese Patent Application Laid-Open No. 4-203421, there are problems of gear noise generated by high speed rotation and a reduction in service life of a bearing due to vibration. In order to reduce the problems relating to the noise and the vibration, it is necessary to improve the working accuracy and the assembling accuracy of the gears, resulting in decreased productivity.
In the structure using the planetary friction roller mechanism described in Japanese Patent Publication of No. 11-502596, there are the following problems a to c in view of the structure thereof for fastening a friction roller such as a planetary wheel and a sun shaft by a flexible outer ring.
a. When the rotation becomes high (i.e., at an impeller rotation speed equal to or greater than 75000 rpm), a slip of the friction roller is generated, and it is impossible to transmit a driving force for supercharging to the impeller.
b. In order to prevent slippage at high speed rotation, it is necessary to increase a force by which the outer ring fastens the friction roller. Accordingly, an undesired fastening force is always applied to the friction roller at low speed rotation, and a driving loss at the low speed rotation is great.
c. In order to prevent slippage at high speed rotation and secure a suitable fastening force at low speed rotation, it is necessary to employ an exclusive assembling step of applying a high working accuracy, a selectable fitting, a suitable shrinkage fitting of the outer ring or the like to the outer ring and the friction roller. As a result, the productivity is deteriorated.
An object of the present invention is to produce a supercharger which does not generate a slip at high speed rotation and a driving loss at low speed rotation, which has low noise and low vibration, which has a light weight and a compact size, and which can be produced at a high productivity.
Another object of the present invention is to improve lubricating and cooling performances of a bearing portion in an output shaft, so as to make it possible to adjust a thrust load and improve durability.
According to the present invention, there is provided a supercharger in which a rotation speed of an input shaft is increased by a speed increasing gear so as to be transmitted to an output shaft, and wherein an impeller is provided in the output shaft.
The speed increasing gear comprises a center roller connected to the output shaft; an outer wheel arranged eccentric to the center roller; and a plurality of intermediate rollers arranged within an annular space in which a width of the center roller with respect to a diametrical direction is uneven with respect to a circumferential direction of the center roller. The annular space is provided between a driven side cylindrical surface corresponding to an outer circumferential surface of the center roller and a drive side cylindrical surface corresponding to an inner circumferential surface of the outer wheel. Respective outer circumferential surfaces of the intermediate rollers are formed as power transmitting cylindrical surfaces.
A pivot of at least one intermediate roller is movably arranged in a circumferential direction and a radial direction of the center roller.